《食品脱水技术》（英文版） 12 Quality Control.pdf_大学文库

LABORATORY ANALYTICAL TESTS Rs aving received samples representative of a batch of finished product, or coming raw material, the staff will carry out the following tests Moisture For moisture tests, either a vacuum oven, set at 70'C, or a fan assisted air oven set at 100-103.C, is used. The former is more accurate, albeit slower, on account of the low temperature used, as this prevents the charring and burning of the sample when it is completely dried out, and allows a more exact result to be calculated Samples of raw vegetable should be grated finely before testing, and dry products should be ground in a small coffee grinder The sample material is dried down to zero moisture, and th weight expressed as a percentage of the original to the nearest 0. 1 percent. Two hours is the average time for drying down most dehydrated vegetables, from 8 percent to zero moisture; raw vegetable samples will take 16 hr. These times apply when using an air oven. A more rapid calculation of moisture in dry products can be made by using an infrared moisture tester. The sample must be finely ground so that it passes through a 10 mesh sieve; a given weight is dried out under an infra red lamp, the loss in weight being recorded by a scale on the tester. Results can be obtained in up to 7min, and in as short a period as 4min for some vegetables These moisture testers, however, are not as accurate as the oven-type, and results can vary about 0.5 percent when compared with the latter. It is nevertheless, an indispensable instrument for the shift chargehand to use for rapid tests on material in course of process, particularly for testing products drying in finishing bins, where it is important for the operator to know the drying end-point accurately, before discharging the material to the packing department Sulphur Dioxide Tests for SO2 concentration are carried out by the Monier Williams method,or what was described in the early days of dehydration as the 'Committee method. The former method is rather more accurate but the latter is more generally used with vegetables, for the sake of speed Basically, the calculation is made by boiling a 20g sample of the ground product in dilute hydrochloric acid and titrating iodine into the distillate as ws 250ml of distilled water are placed in a 500ml flask connected by a splash-head to a vertical condenser terminating in a bubbler feeding into 600ml beake 20g of the dried product for analysis are put into the distilled water in

LABORATORY ANALYTICAL TESTS Having received samples representative of a batch of finished product, or incoming raw material, the staff will carry out the following tests: Moisture For moisture tests, either a vacuum oven, set at 70°C, or a fan assisted air oven, set at 10Oo-103"C, is used. The former is more accurate, albeit slower, on account of the low temperature used, as this prevents the charring and burning of the sample when it is completely dried out, and allows a more exact result to be calculated. Samples of raw vegetable should be grated finely before testing, and dry products should be ground in a small coffee grinder. The sample material is dried down to zero moisture, and the loss in weight expressed as a percentage of the original to the nearest 0.1 percent. Two hours is the average time for drying down most dehydrated vegetables, from 8 percent to zero moisture; raw vegetable samples will take 16 hr. These times apply when using an air oven. A more rapid calculation of moisture in dry products can be made by using an infrared moisture tester. The sample must be finely ground so that it passes through a 10 mesh sieve; a given weight is dried out under an infra red lamp, the loss in weight being recorded by a scale on the tester. Results can be obtained in up to 7min, and in as short a period as 4min for some vegetables. These moisture testers, however, are not as accurate as the oven-type, and results can vary about 0.5 percent when compared with the latter. It is, nevertheless, an indispensable instrument for the shift chargehand to use for rapid tests on material in course of process, particularly for testing products drying in finishing bins, where it is important for the operator to know the drying end-point accurately, before discharging the material to the packing department. Sulphur Dioxide Tests for SO, concentration are carried out by the Monier Williams method, or what was described in the early days of dehydration as the 'Committee' method. The former method is rather more accurate but the latter is more generally used with vegetables, for the sake of speed. Basically, the calculation is made by boiling a 20g sample of the ground product in dilute hydrochloric acid and titrating iodine into the distillate as follows: 250ml of distilled water are placed in a 500ml flask connected by a splash-head to a vertical condenser terminating in a bubbler feeding into a 600ml beaker. 20g of the dried product for analysis are put into the distilled water in 234

the flask, with 10ml of concentrated hydrochloric acid. Heat is applied to bring about boiling in 2-3min. The distillate is collected in 200ml of water in the beaker at the bottom of the condenser, and n/100 iodine is titrated from a burette to maintain a slight excess of iodine. A little starch solution indicator is added to the beaker A marked reduction in the rate of evolution of iodine combining substances is taken as the end-point, or when more than one minute is required to decolorise 0. 2mI N/100 iodine. The distillation should be complete in 5-10min Calculations: Iml N/100 iodine titrated =0.32mgm sulphur dioxide Peroxidase Test for Vegetables During blanching, the enzymes present in active form become progressively inactivated by heat. Of these enzymes, the peroxidase complex is readily perceived because of the colour reaction it promotes with a reagent A suitable reagent is a solution of Guaiacol and hydrogen peroxic made as follows: (1)1 per cent w/v Guaiacol dissolved in distilled water )Mix 25ml of 20 volume hydrogen peroxide in 75ml of water, and add 100ml of 1 per cent Guaiacol solution. The sample for analysis is liberally wetted by the above solution, and the development of a brown colour indicates active, or positive, peroxidase. If the colour is not apparent in one minute, the result is negative, and it can be assumed that blanching is adequate If the result is positive, it is necessary to adjust the blanching conditions, either by increase of temperature or product immersion time Blemish Count A limited number of minor blemishes is often permitted, commercially, in dehydrated vegetables but the tolerance must be rigorously controlled Blemish may arise from disease in the fresh vegetable, skin, root or growth defect, or can stem from a processing fault, such as scorching, under or overblanching, or inefficient peeling Obvious blemish should not be present, and the only tolerated blemish is what is described as ', ie, slight blemish in the dry state, which mainly isappears on reconstitution. The standard will obviously vary from processor to processor but, on of dehydrated vegetable. A similar standard applies to meat in a 50g sample average the permitted tolerance is from 5-7 minor blemishes

the flask, with 10ml of concentrated hydrochloric acid. Heat is applied to bring about boiling in 2-3min. The distillate is collected in 200ml of water in the beaker at the bottom of the condenser, and N/100 iodine is titrated from a burette to maintain a slight excess of iodine. A little starch solution indicator is added to the beaker. A marked reduction in the rate of evolution of iodine combining substances is taken as the end-point, or when more than one minute is required to decolorise 0.2ml N/100 iodine. The distillation should be complete in 5-l0min. Calculations: lml N/100 iodine titrated = 0.32mgm sulphur dioxide. Peroxidase Test for Vegetables During blanching, the enzymes present in active form become progressively inactivated by heat. Of these enzymes, the peroxidase complex is readily perceived because of the colour reaction it promotes with a reagent. A suitable reagent is a solution of Guaiacol and hydrogen peroxide made as follows: (1) 1 per cent w/v Guaiacol dissolved in distilled water: (2) Mix 25ml of 20 volume hydrogen peroxide in 75ml of water, and add 100ml of 1 per cent Guaiacol solution. The sample for analysis is liberally wetted by the above solution, and the development of a brown colour indicates active, or positive, peroxidase. If the colour is not apparent in one minute, the result is negative, and it can be assumed that blanching is adequate. If the result is positive, it is necessary to adjust the blanching conditions, either by increase of temperature or product immersion time. Blemish Count A limited number of minor blemishes is often permitted, commercially, in dehydrated vegetables but the tolerance must be rigorously controlled. Blemish may arise from disease in the fresh vegetable, skin, root or growth defect, or can stem from a processing fault, such as scorching, under or overblanching, or inefficient peeling. Obvious blemish should not be present, and the only tolerated blemish is what is described as ‘minor’, ie, slight blemish in the dry state, which mainly disappears on reconstitution. The standard will obviously vary from processor to processor but, on average, the permitted tolerance is from 5-7 minor blemishes in a 50g sample of dehydrated vegetable. A similar standard applies to meats. 235

Reconstitution Ratio The dried product must be regularly checked for the reconstitution value, in order that correct cooking instructions can be supplied to the ultimate user. A 50g sample is rehydrated and cooked in the prescribed manner and time. The cooking water is drained off, and the drained weight is calculated against the original dry weight, to give a reconstitution ratio. Culinary Report This test is combined with the previous ratio test, and a system of quality marking is implemented and recorded for flavour, texture and colour. The criterion of quality, overall, is that of the freshly cooked fresh vegetable. Bacteriological Tests Dried vegetables must not contain bacteria likely to be harmful to man, and the conditions of manufacture must be such that bacterial toxins cannot be formed. General bacterial counts must be low, and it is the microbiologist’s duty to ensure that factory and personnel hygiene are of a particularly high standard. The use of bactericidal hand creams by operators who handle the raw material - particularly meat and poultry products - is a very essential precaution. Bacteriological equipment required for elementary tests will comprise two incubators (maintained at 37” and 55”C), a good microscope and an adequate supply of Petri dishes for culturing. Meat Product Tests In addition to bacteriological tests, for meat products, there are special tests required to establish free fatty acids, fat content, peroxide value and salt content. Potato Product Tests In addition to the specific tests noted above, for vegetables, tests are made for reducing sugars in raw potatoes and in the dried product in its various forms, and also ‘blue value’ tests to evaluate free starch. Residual Oxygen Test When products are gas packed, tests are made to establish the percentage of residual oxygen in the pack. An Orsat apparatus is required for this, and the commercially accepted standard for residual oxygen in a nitrogen-flushed pack is 2 percent or less. 236

Periodical Tests It is necessary that checks should be made at regular intervals for the presence of arsenic, lead and iron in dehydrated products Metal abrasion is often a source of contamination in a product. This can arise from various items of plant and equipment, hence the necessity for using stainless steel in food handling machinery as far as possible, particularly at the he process. Galvanized iron is sometimes resorted to for equipment in contact with the dry material, mainly on grounds of cost, but this should be kept to a minimum, in view of the contamination risk Arsenic contamination can arise from flue gases, where a direct system of heat is used, but, if proper attention is paid to the use of correct fuels, and the hot air supply is kept clean, this should not give rise to serious problems SPECIFICATIONS Finally, a set of specifications must be established by the technical staff, to cover every product to be handled. It is the duty of the laboratory staff to acquaint production personnel with these specifications, and then evaluate the production samples for compliance Obviously, it is of paramount importance that there is no undue delay in arrying out quality control tests, and it is vital that these run continuously and concurrently with the 24 hour production schedule. Failure to maintain a round-the-clock check can mean considerable quantities of material being turned down as substandard because they do not meet the specification. This can be very costly to the dehydrator, as a salvage operation is not always easy or practicable. Liaison between quality control and production is, therefore, of paramount importance and this cannot be overstressed Bacteriological specifications may well vary, according to the demand of the customer, but the following specification would be generally accepted as the norm Meat Products: Total Count 5000 pet, rom 0.16 Escherichia coli-absent Salmonella species-absent in 25g Vegetables: Total Count,000 per g Maximum Yeast and mould count: 200 per g Bacillus coli-absent from 0. 1g Salmonella species: absent in 25g The complete specification, therefore, will appear under the following headings, against which the Laboratory will report on batch of

Periodical Tests It is necessary that checks should be made at regular intervals for the presence of arsenic, lead and iron in dehydrated products. Metal abrasion is often a source of contamination in a product. This can arise from various items of plant and equipment, hence the necessity for using stainless steel in food handling machinery as far as possible, particularly at the 'wet' end of the process. Galvanized iron is sometimes resorted to for equipment in contact with the dry material, mainly on grounds of cost, but this should be kept to a minimum, in view of the contamination risk. Arsenic contamination can arise from flue gases, where a direct system of heat is used, but, if proper attention is paid to the use of correct fuels, and the hot air supply is kept clean, this should not give rise to serious problems. SPECIFICATIONS Finally, a set of specifications must be established by the technical staff, to cover every product to be handled. It is the duty of the laboratory staff to acquaint production personnel with these specifications, and then evaluate the production samples for compliance. Obviously, it is of paramount importance that there is no undue delay in carrying out quality control tests, and it is vital that these run continuously and concurrently with the 24 hour production schedule. Failure to maintain a round-the-clock check can mean considerable quantities of material being turned down as substandard because they do not meet the specification. This can be very costly to the dehydrator, as a salvage operation is not always easy or practicable. Liaison between quality control and production is, therefore, of paramount importance and this cannot be overstressed. Bacteriological specifications may well vary, according to the demands of the customer, but the following specification would be generally accepted as the norm. Meat Products: Total Count 5000 per g. Escherichia coli - absent from 0.lg. Salmonella species - absent in 25g Total Count - 50,000 per g. Maximum Yeast and mould count: 200 per g. Bacillus coli - absent from 0.lg. Salmonella species: absent in 25g Vegetables: The complete specification, therefore, will appear under the following headings, against which the Laboratory will report on every batch of material: 237